A hot-melt adhesive is solidified for a short period of time. Therefore, it can efficiently attach various kinds of products to each other. Moreover, since the adhesive does not need solvent, it is an adhesive with high safety to the human body and thus is used in various fields. For example, the hot-melt adhesive is used as a sealing adhesive for papers, cardboards and films used for packaging of foods, clothes, electric devices and cosmetic products. In the production of sanitary products such as paper diapers and women's sanitary products, the hot-melt adhesive is used as an adhesive for attaching components constituting them, or as an adhesive constituting an adhesive layer of adhesive tapes or labels.
In general, the hot-melt adhesive is produced by adding a tackifier resin, etc., to a base polymer. In recent years, an attempt to use, as the tackifier resin, a modified hydrocarbon resin obtained by the action of an acid or acid anhydride on a hydrocarbon resin, has attracted attention. It is known that such a modified hydrocarbon resin imparts, to the hot-melt adhesive, novel properties that conventional tackifier resins do not have (water-resistant adhesion, etc.)
For example, Patent Literature 1 discloses a modified hydrocarbon resin having an acid value of from 1 (mgKOH/g) to 150 (mgKOH/g) and a weight average molecular weight of from 300 to 5000 and being obtained by graft copolymerization of a hydrocarbon resin, which is obtained by copolymerization of 100 parts by weight of a vinyl aromatic hydrocarbon with 5 parts to 100 parts by weight of a hydrocarbon mainly composed of a C4-05 unsaturated hydrocarbon, with at least one selected from the group consisting of monoolefindicarboxylic acid and anhydrides thereof. The modified hydrocarbon resin is effective in some adhesives comprising acryl-based base polymers; however, it has poor compatibility with adhesives comprising ethylene-based base polymers or rubber-based base polymers and cannot obtain sufficient adhesion. Also, the modified hydrocarbon resin has a problem of residual monomer-derived odor, since the copolymerization amount of the vinyl aromatic hydrocarbon is large.
Patent Literature 2 discloses an acid-modified hydrocarbon resin which comprises reaction products such as a C5 unsaturated aliphatic hydrocarbon monomer, an isoolefin monomer, and dicarboxylic acid or acid anhydride, and which has a predetermined acid value and a predetermined composition ratio. However, the acid-modified hydrocarbon resin has very poor hue, and the resin has a problem of odor when it is in a hot-melt state at high temperature.